The present invention related to disk drive storage systems and more particularly to a storage system that uses servo track writing.
A typical disk drive storage system includes one or more magnetic disks which are mounted for co-rotation on a hub or spindle. A typical disk drive also includes a transducer supported by hydrodynamic bearing which files above each magnetic disk. The transducer and the hydraulic bearing are collectively referred to as a data head. A drive controller is used for controlling the disk drive based on commands received from a host system. The drive controller controls the disk drive to retrieve information from the magnetic disk and to store information on the magnetic disk. An electro mechananical actuator operates when a negative feedback, closed loop servo system moves the data head radically or linearly over the disk surface for track seek operation and holds the transducer directly above the desired track or cylinder on the disk surface for track following operations.
Information is typically stored in concentric tracks on the surface of the magnetic disk by providing a write signal to the data head to encode flux reversals on the surface of the magnetic disk representing data to be stored. In retrieving data from the disk, the drive controller controls the electro mechanical actuator so that the data head files above the desired track or cylinder on the magnetic disk, sensing the flux reversals on the magnetic disks and generating a read signal based on those flux reversals.
In an embedded servo system, servo information or servo bursts is recorded on data tracks, which also contain stored data. The servo bursts are typically temporally spaced evenly about the circumference of each data track. Data is recorded on a data track between the servo bursts. In a dedicated servo-type system, an entire disk surface and a disk drive is dedicated to storing the servo information.
As the data head reads the servo information, the transducer produces a position signal which is decoded by the position demodulator and presented in digital form to a servo control processor. The servo control processor essentially compares actual radial position of the transducer over the disk (as indicated by the embedded servo burst) with the desired position and commands the actuator to move in order to minimize position error.
The servo information is written on the disk surfaces during the manufacturer of the disk drive module. Each disk drive module is mounted to a servo writer support assembly which precisely locates the disk surface relative to the reference or origin. Each disk drive module is mounted to a servo writer support assembly which precisely locates the disk surfaces relative to reference or origin. The servo writer support assembly supports a position sensor, such as an laser light interferometer, which detects the position of the actuator relative to the disk surface. The position sensor is electronically inserted within the disk drive is negative feed back, close loop servo system for providing position information to the servo system while the servo data is being written to the disk surfaces. The servo writer support assembly may include a clock writer transducer which writes a clock pattern into the disk surface which is used for temporarily spacing the servo data about the circumference of each track.
However, to accomplish writing the servo data, the write heads must be switched very quickly. The servo writer may write one of many surfaces at one time. Additionally, the servo writer verifies by reading with read heads all the surface wedges have been in fact written. Thus, during this read operation, when it is determined that all the servo wedges or servo data has been written, it is necessary to switch very quickly between read heads. Additionally, the read head may be of differing head resistance. However, these read heads operate with differing maximum current or voltage levels and consequently it is necessary to adjust the voltage levels, to accommodate the differing head types to prevent the heads from being destroyed by voltage which exceed those maximum levels. As a consequence the time lost to change the voltage internally so that the heads are not destroyed greatly increases the head switching time.
The present invention includes a constant bias current circuit, which reads information from a head and minimizes the switching while in the servo mode. The circuit of the present invention operates the read heads at a safe operation current which is less than the smallest maximum current among all of the read heads employed. The present invention provides a switching less than 500 nanoseconds and at times can reach 300 nanoseconds for use in the servo mode.